Preprints
https://doi.org/10.5194/acp-2016-289
https://doi.org/10.5194/acp-2016-289

  18 Apr 2016

18 Apr 2016

Review status: this preprint was under review for the journal ACP. A revision for further review has not been submitted.

Complexities in the First Aerosol Indirect Effect over the Southern Great Plains

Sam Pennypacker1 and Allison L. Steiner2 Sam Pennypacker and Allison L. Steiner
  • 1University of Washington, Department of Atmospheric Sciences, Box 351640, Seattle, WA, 98195 USA
  • 2University of Michigan, Department of Climate and Space Sciences and Engineering, Ann Arbor, MI, 48109, USA

Abstract. The aerosol first indirect effect (FIE) is typically characterized by a reduction in cloud droplet size and an increase in cloud optical thickness in the presence of high concentrations of condensation nuclei. Past studies have derived observational evidence of the FIE in specific locations and conditions, yet critical uncertainties in the validity of this conceptual model as it applies to a range of cloud types and meteorological settings remain unaddressed. We utilize five years of surface aerosol measurements and Moderate Resolution Imaging Spectroradiometer (MODIS) observations of cloud properties to discern the FIE in springtime cloud statistics over the Southern Great Plains region of the United States. We extend this analysis to explore the role of three confounding factors: cloud phase, observational uncertainty and the role of regional meridional flow. While high aerosol days are dominated by smaller average droplet size in liquid clouds, the response of cloud optical thickness is variable and is dominantly a function of cloud water path. Ice clouds experience more variability in their response to high aerosol loading and satellite retrieval uncertainty thresholds. Finally, the direction of meridional flow does not play a large role in stratifying the cloud response to different aerosol loading. Overall, these observations show that much of the classical theory for liquid clouds is supported. Higher aerosol loadings are correlated with a reduction in effective radius and generally higher cloud optical thickness, and this relationship dominates over any driving influence from the low-level jet. However, for ice clouds we see a variable response that may be driven by aerosol composition and cold cloud microphysics. These observations provide further insight into the importance of considering deviations from the classic FIE in understanding regional variability in aerosol-cloud interactions in a continental setting.

Sam Pennypacker and Allison L. Steiner

 
Status: closed (peer review stopped)
Status: closed (peer review stopped)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement
 
Status: closed (peer review stopped)
Status: closed (peer review stopped)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Sam Pennypacker and Allison L. Steiner

Sam Pennypacker and Allison L. Steiner

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Short summary
We examine aerosol-cloud interactions detected in springtime cloud statistics over the Southern Great Plains of the United States in the context of cloud phase, measurement uncertainty and regional meteorology. Satellite retrievals of cloud properties are collocated with surface aerosol measurements over five years. The goal is to frame and motivate further work in what could cause deviations from the traditional theory of aerosol-cloud interactions over a given region.
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